On Thu, Jun 28, 2012 at 10:46:58AM -0600, Stephen Warren wrote:
On 06/28/2012 12:18 AM, Hiroshi Doyu wrote:
On Wed, 27 Jun 2012 16:44:14 +0200 Thierry Reding thierry.reding@avionic-design.de wrote:
I think that "coherent_pool" can be used only when the amount of contiguous memory is short in your system. Otherwise even unnecessary.
Could you explain a bit more why you want carveout size on per-board basis?
In the ideal case I would want to not have a carveout size at all. However there may be situations where you need to make sure some driver can allocate a given amount of memory. Having to specify this using a kernel command-line parameter is cumbersome because it may require changes to the bootloader or whatever. So if you know that a particular board always needs 128 MiB of carveout, then it makes sense to specify it on a per-board basis.
Hm...I could understand somewhat;) but DT can also specify "bootargs" in dts file, which can support per-board-wide spec too, like the above sum of carveout needed from all drivers. I just want to avoid introducing a new parameter additionaly if we can make use of the existing mechanism.
The bootargs in the DT file is usually provided by (over-written by) the bootloader. If we start requiring lots of random kernel command-line arguments, that makes it more effort for the user of the bootloader (e.g. distribution bootloader scripts, etc.) to create the kernel command-line. I'd prefer to avoid that as much as possible. That said, using a standardized command-line option that is (or will be) used by all (ARM?) SoCs for the same purpose is reasonable, because there's commonality there.
I propose we stick with the default CMA settings for now and see where we end up. No need to jump the gun.
Thierry